On a recent train, many in-vehicle devices (a propulsion control device, a power-supply device, a brake device, a door device, an air-conditioning device, a toilet device, an ATC device, and the like) are mounted. These vehicle-mounted devices generally include a self-diagnosis function performed by a built-in microcomputer and are connected by a vehicle network (an inter-vehicle network and an intra-vehicle network) for exchanging required information.
As described above, because many in-vehicle devices operate while correlating with each other in a recent train, the importance of time information increases, which each of the devices records for recognizing the correlation therebetween when a failure or an abnormality occurs. Therefore, a means and a method for causing a time error in many in-vehicle devices to be equal to or lower than a predetermined value are desired.
There is a document that discloses a technology for securing the time synchronization between computer systems mounted on a train although the technology does not provide a time synchronization method for many in-vehicle devices mounted on the train (for example, see Patent Document 1).
In the method disclosed in Patent Document 1, a synchronization signal generating unit 3 that generates a synchronization signal is provided. A contact signal line 4 for transmitting the synchronization signal to a synchronization-signal-generated-time measuring unit 5 and a post-synchronization-signal-generation time counting unit 10 is also provided. The synchronization-signal-generated-time measuring unit 5 measures the time at which the synchronization signal is generated based on time data output from a time measuring unit 2, and the post-synchronization-signal-generation time counting unit 10 counts time after the synchronization signal is input. Then, a time calculation processing unit 11 obtains the time measured by the synchronization-signal-generated-time measuring unit 5 and adds the time counted by the post-synchronization-signal-generation time counting unit 10 to the obtained time to calculate the current time.    Patent Document 1: Japanese Patent Application Laid-open No. H06-274243